Fallon, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -0.4 °C (low) to 14.9 °C (high). Annual precipitation averages 351.8 Millimeters. Fallon is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -14.7 °C | -1.4 °C | 7.11 mm |
| February | -12.4 °C | 1.3 °C | 7.87 mm |
| March | -6.6 °C | 7.8 °C | 13.21 mm |
| April | -0.5 °C | 14.7 °C | 36.58 mm |
| May | 5.2 °C | 20.3 °C | 66.8 mm |
| June | 10.7 °C | 25.8 °C | 62.23 mm |
| July | 13.9 °C | 31.3 °C | 50.8 mm |
| August | 12.6 °C | 30.9 °C | 31.75 mm |
| September | 6.7 °C | 24.9 °C | 32.26 mm |
| October | 0.2 °C | 15.8 °C | 25.65 mm |
| November | -6.9 °C | 7.2 °C | 9.4 mm |
| December | -12.7 °C | 0.5 °C | 8.13 mm |
| Annual | -0.4 °C | 14.9 °C | 351.79 mm |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -34.4°C to -31.7°C |
| Plant Hardiness Zone - 2012 | Zone 3b : -37.2°C to -34.4°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |